In the bottling industry, prior art plant for making plastic bottles comprises: a blow-moulding wheel mounted in such a way as to rotate about its longitudinal axis and equipped with at least one blow-moulding unit, which is fed by the blow-moulding wheel around this axis and which comprises two half-moulds, mobile relative to each other between a position of closing and a position of opening at least one cavity for blow-moulding a respective bottle.
The two half-moulds are locked in position by a locking device comprising two locking elements, each mounted on a half-mould and one of which is rotatably coupled to its half-mould and is driven by an electric drive motor to rotate between a position of locking and a position of unlocking the other locking element.
Since the movement of the locking element between its locked and unlocked positions is controlled by the electric motor, the prior art moulding units of the type described above have some disadvantages due mainly to the fact that the absence of electric power supply prevents the locking device from working correctly.
Also known, from document EP1535719 is a solution where the elements for locking the two half-moulds comprise a movable element connected to two elastic elements that can be engaged and disengaged to move the movable locking element in opposite directions.
This solution is also not free of disadvantages, however, since the mechanism that controls the movement of the movable element is complex and not very reliable.